Many currently available prosthetic and orthotic ankle-foot mechanisms do not allow ankle motion. Rigid ankle prosthetic and orthotic ankle-foot devices generally attempt to replace the actions of the biologic ankle-foot system through deformations of their materials and/or by utilizing rocker shapes on the plantar surfaces. The prosthetic and orthotic ankle-foot devices that do incorporate ankle motion usually allow rotational motion about a single point that does not change without mechanical adjustments of the prosthesis or orthosis. Some of these devices use springs and/or bumpers to store and release energy and return the device's ankle joint to one “equilibrium” point. This single and constant “equilibrium” point can result in good function on level terrain and when using shoes of one particular heel height (heel and forefoot sole differential). However, problems can arise when walking on different terrain or when using shoes of different heel height. The heel height problem can be fixed using a change in the alignment of the prosthesis. However, this is not a simple task and one that does not happen automatically.
A patent issued to Wayne Koniuk (U.S. Pat. No. 6,443,993 B1, “Self-Adjusting Prosthetic Ankle Apparatus”, issued Sep. 3, 2002) discloses a device that will adapt to various terrains and to shoes of different heel height. However, Koniuk's design does not appear to have energy storage and release properties, utilizes more sensing devices than the proposed design, and does not appear to give plantarflexion at late stance. Koniuk's design is based on damping control of the ankle joint whereas the proposed device is based on the control of stiffness about the ankle. Damping removes energy from a system whereas stiffness can store and release energy to a system throughout a loading and unloading cycle (that is, a walking cycle).
Recent research has suggested that roll-over shape, the effective rocker shape that the ankle-foot system conforms to between heel contact and opposite heel contact, is an important characteristic for walking. Hansen ((2002); “Roll-over Characteristics of Human Walking With Applications for Artificial Limbs.” Ph.D. dissertation, Northwestern University, Evanston, Ill.) found that the able-bodied ankle-foot system adapts to several walking conditions to maintain a similar roll-over shape and that its roll-over shape changes predictably when walking on inclined or declined surfaces. Specifically, able-bodied ankle-foot systems are capable of automatically adapting to differences in shoe heel height and to different surface inclinations. Current prosthetic ankle-foot mechanisms cannot automatically adapt to these conditions.
The prior art demonstrates that there is a current and long-felt need for an improved ankle prosthesis or ankle-foot prosthesis or orthosis that can better emulate the gait of an able-bodied individual and adapt to the terrain on the first step.